Sink insert



FIG. 1 is a top plan view of a sink insert showing my new design;

FIG. 2 is a side elevational view thereof, the opposite side being the same as the side shown;

FIG. 3 is a front elevational view thereof, the rear being the same as the front shown;

FIG. 4 is a bottom plan view thereof; and,

FIG. 5 is a top perspective view thereof.

The broken line representation of a sink in FIG. 5 is for purposes of illustration only and forms no part of the claimed design. 

The ornamental design for a sink insert, as shown and described. 